The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
A multi-speed transmission can use a combination of clutches, planetary gear arrangements, and fixed interconnections to achieve a plurality of gear ratios. In one example, friction type clutches are used in the transmission, and are selectively engaged to achieve a particular gear ratio. However, when disengaged, friction clutches tend to produce drag when there is relative motion between the clutch input member and the output member, which can lead to decreased fuel economy.
In an effort to improve fuel economy, a one-way clutch may be selectively employed instead of a friction clutch to transmit power from a first input member to a second driven member. Known one-way clutches transmit torque in a first rotational direction and release or decouple in a second, opposite rotational direction. Once released, the driving member is free to rotate in the second opposite direction relative to the first direction, and the one-way clutch can overrun or freewheel. This allows the vehicle to travel in a coasting or gliding mode where the drivetrain is decoupled from the engine, thus eliminating any losses associated with the drivetrain turning the engine.
Engine braking occurs when torque to the driving member is reduced, but the driving member and the driven member remain coupled to one another. Back torque as a result of turning the engine with reduced power and pumping forces is therefore transmitted in an effort to reduce the speed of the driven member. However, freewheeling known one-way clutches either decouples the driven and the driving member, thereby making engine braking not possible, or the spring biased struts used to provide one-way rotation may bind, preventing release from the coupled condition. Thus, engine braking in a vehicle operated with known one-way clutches does not work unless additional components are included, such as an additional member activated to selectively de-couple the driving member from the driven member.
Thus, while current transmissions achieve their intended purpose, there is a need for a new and improved transmission which exhibits improved performance while allowing engine braking.